Volvo Repair: S70 a/c intermittent, prybar, switch works

Question
QUESTION: 1998 S70, non turbo, ECC. The a/c will blow cold then the clutch will disengage intermittently from minutes to hours, when this happens I can ground the a/c relay terminal #2 and it works. This wire goes to ECM pin #40.One other thing, terminal #2 has power when the a/c is inop, and shows ground when the a/c is working fine.The rest of the a/c is not affected, I've made sure the low pressure switch works.Seems to me to be ECM or ECC,can you help? I don't know these systems or their common problems.
Thanks, Mike

ANSWER: Mike, did you check the A/C refrigerant levels first?  On these cars what happens is the Clutch clearance gets too wide.  Next time it stops, get out and carefully tap on it with a prybar and see if it will engage.  If it does, then you have 3 choices.  New clutch, new compressor or take the front part of the clutch off and remove one of the shims.  Pesonally, if you are going to take the time to mess with that, in the long runs its cheaper to replace the compressor.  The clutch alone is almost 200 bucks.  Hope this helped.  I havent seen one of those heads go bad on the 98's.  93-97 goes bad constantly.  Roger

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QUESTION: Roger,
The refrigerant levels are good, tapping on the clutch doesn't help ( no power to the clutch when the problem is their),shorting out the low pressure switch doesn't help. I know the problem is in the control side of the a/c clutch relay which is controlled by the ECM pin#40, but I'm lost after that.

Thanks,
Mike

Answer
Mike, I have taken apart the 940 heads and there is a problem with a bad solder joint.  There may be a chip is burned on that one.  I would see if its possible to open it up and take a look inside.  Perhaps smell it to see if it smells burnt.  Other than that, I would have to see the car and run a few tests of my own.  Roger